The invention relates to a method for producing a cast part of a thermal turbo-machine. More particularly, the invention relates to a method for producing a cast part with recesses created by projection on a ceramic insert, and to a metal mold with a ceramic insert and a ceramic insert having such projections.
Cast parts of thermal turbo-machines are produced using known casting processes. Casting furnaces for such casting processes are disclosed, for example, in EP-A1-749 790, U.S. Pat. Nos. 3,763,926 or 3,690,367.
A method for producing a complex part of a gas turbine using a casting mold is known, for example, from U.S. Pat. No. 5,296,308. A wax model of the hollow part to be cast is produced with a model mold and a ceramic insert. After this, this model mold is removed, and a ceramic casting mold is formed around the wax model with a slip. Once the wax has been burned away, the cast part can be produced using one of the above-mentioned casting processes. It is suggested in U.S. Pat. No. 5,296,308 to provide projections on the ceramic insert. On the one hand, this is supposed to ensure that the wall thickness of the part to be poured is within a certain tolerance range. On the other hand, it makes it possible to ensure the fixation of the ceramic insert in the casting mold during the casting process. The use of these projections for the mentioned purposes was generally found to be advantageous.
However, the projections also have side effects that are not very advantageous. In the wall of the casting part, recesses are created by these projections. So far, the notch factor of these recesses has been relatively large. The disadvantage is that these recesses therefore can only be positioned in certain areas on the component surface, since tensions acting during operation on the component could potentially be too large, possibly creating tears in the affected components.
The invention is based on the objective of creating a method for producing a cast part of a thermal turbo-machine using a known casting process, wherein the casting mold of the cast part is produced with a wax model and a ceramic insert, and whereby projections are provided on the insert, which reduces the notch factor at the recesses of the cast part that are created by the projections of the insert. A further objective is to create a model mold and a ceramic insert for this method.
According to the invention, this objective is realized with a method for producing a cast part in that on the cast part, recesses are created by the projections of the ceramic insert, whereby the projections have an angle between the center line and outer edge of the projections of less than 30xc2x0. The objective is furthermore realized with a model mold comprising a ceramic insert having a plurality of projections and positioned in a wax model during a casting process, and a ceramic insert comprising at least one projection on a surface. The projections have an angle between the center line and outer edge of the projections of less than 30xc2x0.
This advantageously reduces the notch factor of the recesses created on the cast part. The notch factor is reduced even further if the angle between the center line and outer edge of the projections is less than 15xc2x0. The projections can be positioned at places of the cast part where this was not previously possible because of increased tensions during operation. A higher density of the projections can be achieved. An improved distribution or increased number of projections improves the fixation of the ceramic insert in the model mold or in the ceramic casting mold during the casting process. According to another exemplary embodiment, the angles on different sides of the projection are of different sizes, i.e., have different values.
An advantageous embodiment exists if the projections project into the model mold. This, for one, achieves a clearer contour of the edges of the recess. The movement of the ceramic insert parallel to the wall of the cast part is possible to a certain extent. This can prevent a breaking of the ceramic insert through thermal tensions that act on it during the casting process. This objective is achieved better by realizing the recesses on the model mold into which the projections are projecting with a flat base.
In order to further reduce the notch factor at the recesses, it is advantageous to cut out or erode out the recesses created on the cast part because of the projections from the outer side of the cast part, in part in conical or cylindrical shape. Into the recess of the cast part, a cylindrical, conical or round pin is attached. This pin, for example, may be soldered or welded. The closing off of the recesses prevent the cooling air from exiting. Another advantage of the closure is that it prevents a local overheating of the edges of the recess. This may occur when cleaning coated blades, for example by means of arc cleaning.